<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>CSS进度条</title>
</head>
<style>
    .bar {
        width: 150px;
        height: 15px;
        border: 1px solid red;
        border-radius: 7px;
        padding: 1px;
    }
    
    .bar_in {
        width: 50%;
        height: 100%;
        background-color: red;
        transition: all .7s;
    }
    
    .bar:hover .bar_in {
        width: 100%;
    }
</style>

<body>
    <div class="bar">
        <div class="bar_in"></div>
    </div>
</body>

</html>